Effects of maple syrup urine disease metabolites on mouse L-fibroblasts in vitro: a fine structural and biochemical study

Primary human fibroblasts from a maple syrup urine disease patient undergo apoptosis following exposure to physiological concentrations of branched chain amino acids

Maple syrup urine disease (MSUD) is an inborn error of metabolism caused by a deficiency in branched chain alpha-ketoacid dehydrogenase. We have recently found that MSUD neurodegeneration may result, at least in part, from apoptosis triggered by branched chain amino acids and their alpha-ketoacid derivatives. In the present study, we investigated the sensitivity of MSUD fibroblasts to defined mixtures of MSUD metabolites. Defined combinations of MSUD metabolites, at levels comparable to those in MSUD patients, triggered cell death in skin fibroblasts from a MSUD patient, while control fibroblasts were resistant. The mechanism of cell death was confirmed as apoptosis by in situ end labeling.

Branched chain amino acids induce apoptosis in neural cells without mitochondrial membrane depolarization or cytochrome c release: implications for neurological impairment associated with maple syrup urine disease

Maple syrup urine disease (MSUD) is an inborn error of metabolism caused by a deficiency in branched chain alpha-keto acid dehydrogenase that can result in neurodegenerative sequelae in human infants. In the present study, increased concentrations of MSUD metabolites, in particular alpha-keto isocaproic acid, specifically induced apoptosis in glial and neuronal cells in culture. Apoptosis was associated with a reduction in cell respiration but without impairment of respiratory chain function, without early changes in mitochondrial membrane potential and without cytochrome c release into the cytosol. Significantly, alpha-keto isocaproic acid also triggered neuronal apoptosis in vivo after intracerebral injection into the developing rat brain. These findings suggest that MSUD neurodegeneration may result, at least in part, from an accumulation of branched chain amino acids and their alpha-keto acid derivatives that trigger apoptosis through a cytochrome c-independent pathway.